The present invention relates generally to modulating light and, more particularly, to a circular polarization modulator which outputs light alternating in time between left-hand and right-hand circular polarization using controllable birefringence.
Lasers and other light sources have been used in a variety of systems and devices for many years. For example, light has been used as the basis for imaging, generating signals in optical fibers, increasing the speed of communication systems, enhancing the recognition, detection and classification capabilities of targeting systems as well as enabling other novel devices and systems.
One key aspect to the implementation of light based technology lies in the capabilities of the light source employed. As such, laser devices have been continually modified and refined to perform more precise and reliable functions. To expand the applicability of developed laser technologies, devices such as modulators have been designed and employed.
In this area of laser technology, modulators such as inorganic electro-optic crystal modulators, voltage-induced liquid-crystal reorientation modulators and photoelastic effect based fused-silica plate modulators have been used to expand the applicability of a given laser through polarization modulation. Despite the advantages of these technologies, each has design limitations which prevent broad acceptance. For example, inorganic electro-optic crystal modulators typically require driving voltages in the kilovolt range and use capacitive electrodes which have RC-time-constant limitations. Voltage-induced liquid-crystal reorientation modulators are often bulky, cannot be implemented in an integrated optics application, generally require careful mechanical assembly and are limited to modulation speeds of a few kHz. Photoelastic effect based fused-silica plate modulators, like voltage-induced liquid-crystal reorientation modulators, are generally bulky, have fixed modulation speeds in the range of 20-100 kHz and lack adaptability for integrated optics approaches.
These current laser modulation technologies are also generally incompatible with the ever shrinking electronic components being fabricated today. Without the ability to integrate laser modulation technology into smaller devices, laser technology may become obsolete for many current needs. Existing uses of laser technology as well as such uses as polarimetry of materials, polarization sensitive imaging and high speed polarization scrambling of signals in optical fibers will likely be forced to seek alternatives in order to avoid the limitations of current laser modulation implementations.
In accordance with teachings of the present invention, a circular polarization modulator is provided. In one embodiment, the circular polarization modulator includes a waveguide core and a cladding material disposed on a first surface of a substrate. The waveguide core preferably includes first, second and third core regions formed in the cladding material disposed on the first surface of the substrate. The first, second and third core regions may be formed as part of a single uniform waveguide core or as separate, individual components optically coupled with each other to the waveguide core.
To induce a mode-conversion effect in the first waveguide region, a DC voltage source coupled to a first electrode on the first surface of the substrate and to a second electrode on a first surface of the cladding material is preferably included. An AC voltage source may also be coupled to a third electrode on the first surface of the substrate and to a fourth electrode on a first surface of the cladding material such that a wave retardation effect in the second waveguide region is created. The use of patterned electric field poling both in location and orientation including the absence of any poling provides the unique character of the first, second and third waveguide regions. The first waveguide region is tilt poled, the second waveguide region is vertically poled, and the third waveguide region is not poled.
In another embodiment, a circular polarization modulator including a waveguide having at least one electro-optic segment suspended in at least one layer of cladding material on a top surface of a substrate is provided. A DC voltage source preferably coupled to a first electrode on the top surface of the substrate and to a second electrode on the top surface of the cladding material such that a tilt-poled effect is created in a first region of the waveguide is also preferably provided. An AC voltage source coupled to a third electrode on the top surface of the substrate and to a fourth electrode on the top surface of the cladding material such that a wave retardation effect is created in a second region of the waveguide is also preferably provided.
In yet another embodiment, a method for creating circular polarized light by inducing a tilt-poled region in a waveguide, inducing a wave retarding region in the waveguide and transmitting light through the waveguide is provided.
The present invention provides technical advantages of small mass, low power consumption, compact alternative as compared to bulky and expensive polarization modulators such as liquid-crystal and inorganic-crystal polarization modulators.
The present invention provides further technical advantages through elimination of moving parts, use of low voltages and, preferably, a single high-speed voltage source. For some applications, a polarization modulator formed in accordance with teachings of the present invention can polarize or rotate a light signal through one hundred eighty degrees (180xc2x0) and back or through a complete three hundred and sixty degree (360xc2x0) circle.
Another technical advantage provided by the present invention is the ability to use light sources having wavelengths varying from 700 nanometers (nm) to 1600 nm on a given circular polarization modulator as determined by the specific polymer material used.
The present invention further provides technical advantages associated with operating at frequencies in the GHz range.
A technical benefit of the present invention includes the use of patterned poling which eliminates or substantially reduces the use of lenses or other optical devices to direct light from one waveguide to another.
The use of electro-optic polymer in conjunction with patterned poling eliminates or substantially reduces problems associated with waveguides and polarization modulators formed in part from inorganic-crystals such as lithium niobate or lithium tantalite.